Add the ability to choose a video mode for the selected gop by using a
command-line argument of the form
	video=efifb:mode=<n>
Signed-off-by: NArvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-12-nivedita@alum.mit.eduSigned-off-by: NArd Biesheuvel <ardb@kernel.org>